Chapter 8: Neural Physiology

Events Occurring in an Action Potential

An action potential is a rapid, temporary change in a cell's membrane potential, essential for nerve impulse transmission.

• Ion Permeability and Ion Flow: During an action potential, the membrane's permeability to sodium (Na+) and potassium (K+) changes, leading to characteristic voltage changes across the membrane.

• Voltage-Gated Na+ Channels: These channels open rapidly in response to depolarization, allowing Na+ influx, and then inactivate shortly after.

• Depolarization Progression: Depolarization occurs as Na+ enters the neuron, making the inside more positive. This is followed by repolarization as K+ exits the cell.

• Conduction in Axons: In unmyelinated axons, action potentials propagate continuously along the membrane. In myelinated axons, action potentials "jump" between nodes of Ranvier in a process called saltatory conduction, which increases conduction speed.

Absolute vs. Relative Refractory Periods:

• Absolute Refractory Period: No new action potential can be initiated, regardless of stimulus strength, due to inactivation of Na+ channels.

• Relative Refractory Period: A stronger-than-normal stimulus can initiate another action potential, as some Na+ channels have reset but K+ channels remain open.

Neurotransmitter Release at Chemical Synapses

• Triggering Release: Neurotransmitter (NT) release is triggered by the arrival of an action potential at the axon terminal, causing voltage-gated Ca2+ channels to open and Ca2+ influx, which stimulates vesicle fusion and NT exocytosis.

• Amount of NT Released: The amount of NT released depends on the frequency of action potentials and the amount of Ca2+ entering the terminal.

• Effect on Postsynaptic Neuron: NTs can cause either depolarization (excitatory postsynaptic potential, EPSP) or hyperpolarization (inhibitory postsynaptic potential, IPSP) in the postsynaptic neuron.

Key Terms:

• Depolarization: Membrane potential becomes less negative (more positive).

• Hyperpolarization: Membrane potential becomes more negative.

Chapter 9: Central Nervous System (CNS) Organization

Gray Matter, White Matter, Tracts, and Nuclei

• Gray Matter: Contains neuron cell bodies, dendrites, and unmyelinated axons. Found in the cerebral cortex and central spinal cord.

• White Matter: Composed of myelinated axons forming tracts that connect different CNS regions.

• Tracts: Bundles of axons in the CNS, classified as ascending (sensory) or descending (motor).

• Nuclei: Clusters of neuron cell bodies within the CNS.

Cerebrospinal Fluid (CSF) and Blood-Brain Barrier

• CSF: A clear fluid produced by the choroid plexus in the ventricles; cushions the brain and spinal cord, removes waste, and provides nutrients.

• Blood-Brain Barrier: A selective barrier formed by endothelial cells and astrocytes that restricts passage of substances from blood to CNS tissue.

Spinal Cord Organization

• Dorsal Roots: Carry sensory (afferent) information into the spinal cord.

• Ventral Roots: Carry motor (efferent) information out of the spinal cord.

• Gray Matter Horns: Dorsal, lateral, and ventral horns process different types of information.

• White Matter Tracts: Ascending tracts carry sensory information; descending tracts carry motor commands.

Brainstem and Diencephalon Functions

• Medulla: Contains pyramids (motor tracts); controls vital functions like heart rate and breathing.

• Pons and Midbrain: Involved in respiration, sleep, and sensory/motor relay.

• Cerebellum: Coordinates movement and balance.

• Diencephalon: Includes the thalamus (sensory relay), hypothalamus (homeostasis, hormone regulation), and pituitary gland (hormone secretion).

Hormones and Functional Areas of the Cerebral Cortex

• Anterior Pituitary Hormones: Some are tropic (stimulate other endocrine glands). Hypertrophy is tissue growth; atrophy is tissue shrinkage.

• Posterior Pituitary Hormones: Includes oxytocin and vasopressin (antidiuretic hormone, ADH).

• Functional Areas:

  • Primary Motor Cortex: Controls voluntary movement.

  • Primary Somatosensory Cortex: Processes touch, pain, temperature.

  • Primary Visual Cortex: Processes visual information.

  • Primary Auditory Cortex: Processes sound.

  • Primary Olfactory Cortex: Processes smell.

  • Primary Gustatory Cortex: Processes taste.

Chapter 10: Sensory Physiology

Transduction and Sensory Receptors

• Transduction: The process by which sensory receptors convert stimulus energy into electrical signals (membrane potential changes).

• Modality: The type of stimulus (e.g., light, sound, touch) detected by a receptor.

• Neural Receptors: Can be myelinated or unmyelinated; transmit information about specific modalities.

• Nonneural Receptors: Specialized cells that synapse onto sensory neurons.

Key Terms and Concepts

• Adequate Stimulus: The specific type of stimulus to which a receptor is most sensitive.

• Threshold: The minimum stimulus intensity required to generate a response.

• Receptor Potential: Graded potential produced in a receptor cell by a stimulus.

• Receptive Field: The area monitored by a single sensory neuron.

Major Groups of Receptors

• Mechanoreceptors: Respond to mechanical forces (touch, pressure).

• Thermoreceptors: Detect temperature changes.

• Chemoreceptors: Respond to chemical stimuli (taste, smell).

• Photoreceptors: Detect light (in the retina).

Sensory Pathways and Processing

• Ascending Pathways: Sensory information travels to the brain via spinal tracts or cranial nerves.

• Perceptual Thresholds: The level at which a stimulus is strong enough to be perceived.

• Habituation: Decreased response to a repeated, benign stimulus.

• Lateral Inhibition: Enhances contrast and spatial resolution by inhibiting neighboring neurons.

• Tonic vs. Phasic Receptors: Tonic receptors adapt slowly and respond for the duration of a stimulus; phasic receptors adapt quickly and respond only to changes.

Somatic Sensation and Pain

• Somatic Sensation Pathway: Sensory information is relayed from receptors to the somatosensory cortex via primary, secondary, and tertiary neurons.

• Nociceptors: Pain receptors located throughout the body; respond to mechanical, thermal, or chemical stimuli.

• Fast vs. Slow Pain: Fast pain is sharp and transmitted by myelinated Aδ fibers; slow pain is dull and transmitted by unmyelinated C fibers.

• Referred Pain: Pain perceived at a location other than the site of the stimulus, due to convergence of sensory pathways.

• Pain Modulation: Involves inhibitory interneurons and descending pathways that can suppress pain signals (e.g., gate control theory).

Gate Control Theory of Pain

• Gate Control Theory: Proposes that non-painful input (e.g., touch via Aβ fibers) can inhibit pain transmission by activating inhibitory interneurons in the spinal cord, thus "closing the gate" to pain signals from C fibers.

Additional info: Some details, such as specific neurotransmitters, hormone names, and exact neural pathways, may require further study from lecture materials or textbooks for full mastery.